First there were some complaints against SK Telecom and KT about blocking VoIP over mobile (here); Then KT CEO said that "OTT Providers should Pay or will see a big data blackout" (here). Last month SK Telecom's Head of SKT’s Technology Strategy Office said that "Korean mobile carriers are experiencing difficulties, including decreased SMS revenues and increased network investment cost to accommodate surging traffic, caused by the popularity of various free messaging services ..KaKao Talk, a mobile messaging service used by 37 million Koreans (46 million subscribers globally as of May 2012), is fast becoming a threat to mobile operators as it has recently launched a mVOIP service".
Yewon Kang reports to IT World that ".. the Korea Communications Commission said last week that it will let three local mobile operators, SK Telecom, KT and LG U+, charge users extra fees for VOIP applications or block their use entirely .. SK Telecom and KT currently offer unlimited data plans, which allow users to freely download apps on their networks, whereas LG U+ used to block over-the-top programs entirely .. The companies have not yet released specific information on their new rates .. Unofficially, the KCC has already permitted telecoms to enact policies of their choice regarding third-party apps, experts say".
See "South Korean telcos get OK to charge extra for mobile VOIP apps" - here.